Reversible cycle heat pumps are utilized in applications requiring both heating and cooling functions, and these systems include the reversible cycle vapor compression refrigeration approach. Such systems employ two heat exchangers, one located inside the controlled volume and one located outside. The flow of refrigerant through these heat exchangers is reversible. With flow in a first direction, the system carries heat outside resulting in cooling of the controlled volume. With flow in the second direction, opposite to the first direction, the system carries heat inside resulting in warming of the controlled volume.
Refrigerant flow through the system is induced by a compressor. Because the compressor can only pump in one direction, a valving arrangement directs the refrigerant from the non-reversible compressor section into the reversible section containing both heat exchangers. In the non-reversible section, the refrigerant in the line leading to the compressor is in a gaseous, or vapor, state.
In the reversible section, there are two primary carrier lines transferring refrigerant between the heat exchangers. One line serves as a continuation of the vapor line feeding the compressor and may carry saturated refrigerant. This line and its continuation into the non-reversible section are called the suction line. The other primary carrier line in the reversible section carries liquid refrigerant and is called the liquid line.
During cooling operations, it is desirable to utilize a liquid line to suction line heat exchanger to improve cooling efficiency. In the cooling mode, the suction line carries gaseous refrigerant returning to the compressor from the inside heat exchanger. The liquid line carries liquid refrigerant from the outside heat exchanger, through the expansion device, to the inside heat exchanger. In this mode, a liquid line to suction line heat exchanger can improve system efficiency by using the remaining heat absorption capability of the vapor to lower the temperature of the liquid.
U.S. Pat. No. Re. 32,092 to Davis discloses a liquid line to suction line heat exchanger for use in a standard, that is, non-reversible, compression vapor refrigerant system. This heat exchanger provides higher operating efficiencies than for the same system operating without the Davis device. However, if the Davis device is used in a reversible cycle heat pump system, it would transfer heat in the other direction during heating operations. Such heat exchange is widely known to be detrimental to performance in the heating mode.
U.S. Pat. No. 4,236,381 to Imral, et al. discloses a liquid line to suction line heat exchanger for use in a heat pump that is intended to work primarily during heating operations. This design is intended for use in systems that do not accomplish full evaporation of the refrigerant in the exterior heat exchanger during heating operations. The goal of the Imral device is to protect the compressor from slugs of liquid refrigerant.
This design has three disadvantages. First, it effects heat exchange during the heating cycle which is detrimental to heat output. Second, it does not operate effectively nor is it intended to operate effectively during the cooling cycle. Third, it relies on vertical orientation to operate properly. Therefore, it could not operate reliably on airplanes, surface vessels, submarines, or spaceships, where vertical orientation or even gravity may not be constant or reliably available.
It is a goal of the present invention to provide a liquid line to suction line heat exchanger for use in a reversible cycle heat pump system which can be selectively used during the cooling cycle to improve system efficiency and selectively not used during the heating cycle so as to in no way be detrimental to system operation.
It is a further goal of this invention to provide a device which works in any spatial orientation.
It is still another goal of this invention to provide a device which may be either actively or passively controlled.